To investigate the association of polyQ diseases with the risk of cancer, Jianguang Ji, MD, from Lund University in Sweden, and colleagues analyzed data from 1,510 patients with Huntington's disease (HD), 471 with spinobulbar muscular atrophy (SBMA), and 3,425 with hereditary ataxia (HA), identified from 1969–2008 in Sweden. Data were linked to the Swedish Cancer Registry to calculate standardized incidence ratios for cancer and compare the risk with that of the general population.

The researchers found that cancer was diagnosed in 12.3% of patients with HA, 7.2% with SMBA, and 6% with HD; with standardized incidence ratios of 0.77, 0.65, and 0.47, respectively. The risk of cancer was even lower prior to diagnosis of polyQ disease. The risk of cancer and cancer incidence in unaffected parents of patients with polyQ were comparable to that seen in the general population.

"In this large study, we found that incidence of cancer, overall and for specific sites or types, was significantly lower in patients with polyQ diseases than in the general population," the authors write. "Future studies should investigate the specific biological mechanisms underlying the reduced cancer risk in patients with polyQ diseases."